Electric spark-plug.



. TED T i I CHARLES KNOX HARDING, OF CHICAGO, WON.

' ELECTRIC SPARK-PLUG.

110 Drawing.

insulating from each other the metallic conducting electrodes which are usually carried in a suitable metal shell detachably screwed into an opening in the wall of internal combustion engines.

This invention relates particularly to a new class of non-carbonizing spark plugs which are required to operate at an extremely high temperature, such as described in my United States Patent No'.,1,272,431, July 16th, and No. 1,27 5,020, Aug 6, 1918.

The insulating material most commonly used for spark plug insulators is porcelain and its defects at high temperatures are well lmown. Among them may bementioned its low, dielectric insulating properties at high temperatures, and this I believe is caused by the heterogeneous character of the highly .acid and extremely basic oxids, such as silica, SiO on the one end and alkalis as potash K 0 at the extreme opposite end of the series of which all vitreous earthenware insulators have heretofore been made.

I have discovered that the refractory oxids of which a much improved spark plug insulating structure is formed should be neutral, or very nearly neutral, and not be subject to form eutectic compounds of widely varying basic vand acid slag-forming and easil electrolized character. The oup of suitable neutral oxids will be specifically described hereinafter.

The theoretical assumption-that viscous fused the I vitrified as distinguished from the crystalline form is when cold composed of very large condensed aggregates of enormous molecular weight, each consisting of a large number of silica molecules polymerized and forming a large molecular compound unit carrying equally balanced positive and negative charges or electrons-and that these polymerids gradually break up into smaller masses with comparative small Specification of Letters Patent.

Patented Mar. 4, 1919.

Application filed June a, 1918. Serial No. sas es.

increase of temperature without any marked change in the physical character of the mass or structure of which they form a part, this theory is confirmed by the fact that ceramic bodies containing fused silica such as porcelain, earthenware, etc, show an almost constant increase of electric conductivity with increase of temperature so that an increase of temperature of as little as 25 or 50 degrees Fahr. will double the conductivity-presumably by doubling-the number of polymerized charge-carrying masses-and the regular falling to half the value of the resistance with each equal addition of heat so that from any temperature-the increase through six of these intervals would reduce the insulating value proportionately to the sixth power of two, or by sixty-four times these changes go on in all ceramic structures containing polymerized silica molecules several hundred degrees below any fusing or softening point of the body of which the insulator is made. These considerations have aided in the discovery of my improved spark plug in which the insulating structure is formed from oxids of chemically neutral elements of high atomic weight, 71. e., from 90 to 232,

so that insulators containing a given weight of oxids contain only from one-half to one fourth as many molecules as would be the case if their mass was made up of oxids of aluminum or silicon.

The most neutral of'the known earth oxids is lanthanium mud. The dydimiums are next which are almost equally neutral and'do not tend to flux or form silicates while the next closest of the most neutral group on the one side is zirconium oxid and thorium oxid on the other which are almost neutral but will form silicates. My experiments have demonstrated that lanthanium oxid and compounds thereof when forming the principal constituents of refractor ceramic insulating structures, such as spark plug insulators, produce an improved insulator superior to anything heretofore known or.used for the purpose where the insulator was operated at high temperature.

A careful examination of all the noncombustible insulators known or; used up to the year A. D. 1915, including steatite, mica,

and all kinds of porcelain and earthenware This silica or flint necessarily carries into the structure too much of its friable, frangible, fragile and other undesirable properties for a body required to withstand sudden and extreme changes of temperature.

The object of my invention was to overcome the defects attributable to silica. I have therefore endeavored to discover or devise a new insulating body as free as possible from silica, and my invention is therefore that of a new and improved spark plug insulator characterized by the absence of a substantially objectionable content of silica.

The potters art for more than a thousand years has been based on silica and clay-a double silicate of aluminum-but I have by going outside this art produced scores of difierent refractory ceramic structures containing no clay or aluminum and no silica in any form.

The preferred substance from which to construct the most desirable spark plug insulator, so far as I am at present aware, is one containing an excess of lanthaniumoxid over and above any lanthanium compound it may contain and in excess of a varying quantity from 10 to.40 per cent. of lanthanium phosphate which it may contain without disadvantage. The highest purity is not required and oxids of the other neutral elements may be added or left in the partly refined lanthanium compound, which is most conveniently obtained from the mineral, monazite, which usually contains about 90% of phosphates of the cerite group of rare earths, from which when the twentyeight parts of phosphoric acidis removed there remains about 62% of the oxid of praseodymium, cerium, neodymium and lanthanium by what is known as the hydrated sulfate method of separation. Lanthanium hydrated sulfate La (SO 9 (H O), which is by far'the least soluble of this group of hydrated sulfates, can be separated in one or two treatments of suflicient purity for use in my improved spark plug insulator. The

I mixed anhydrous sulfates produced by heat-' ing until all the water and excess acid is driven off, is dissolved in about eight parts ice water and then gradually heated until the hydrates form; the various hydrates have varying solubility in the order named above; that is, praseodymium is about seven times as solubleas lanthanium, the hydrated sulfate of cerium Ce (SO )58(H O) about five times as soluble, and neodymium about three and a half times as soluble, so that the first of the precipitate is largely the lanthaniun salt. At a little higher temperature the precipitate contains more neodymium, while at a still higher temperature the cerium will become lesss oluble and considerable cerium will separate with the precipitate.- I have not been able to determine as yet exactly 'what is the best proportion of these rare earth oxids for a spark plug in sulator, but experiments indicate a certain amount of both cerium and dymium oxids is desirable, and it reduces the cost of manufacture to include them in the body of the insulator.

Thorium oxid should not be present in all parts of the insulator in excess as its ionizing efi'ect tends to reduce the dielectric resistance of a film of air at the surface of the insulator.

Most of the processes of the potters art for forming earthenware structures depend ing on capillary and colloidal water shrinkage to draw the body into a dense compact masscannot be employed with lanthania or neutral rare earth oxidsbut mixtures of such oxids containing .no clay may be formed to the desired shape by so-called dry forming; that is compressing slightly moist materials in steel molds under very heavy pressure.

Finely ground. calcined lanthania-'with air dry lanthanium phosphate and6 to 12 per cent. gelatinous lanthanium hydratemay be subjected to a high pressure in a metal die and formed into a very compact structurethat will not check in air dry ing-and may be fired to a very high tem perature above Segar cone '20 without inury.

If difficulty is met in reducing the porosity of the formed insulator to the required'densityit may be rendered dense and impervious-by impregnating the body with a strong solution of soluble salts of the suitable earths-nitrate, chlorid, etc., of zirconium or the rare earth elements-then drying and refiring to some attainable temperature-eutectic mixtures-of the oxids and'phosphates of the rare earths may be formed that will vitrify sufficiently at temperatures between cone 16 and 20.

This process may be varied by saturating the insulator at any stage where it remains to any extent pervious with acid solution of earthy oxids containin excess phosphoric .acid'or alternate app ications of nitrates which leave only diificultly vitrifiable oxids deposited in the structure may be followed by acid solutions containing an excess of phosphoric acidwhich react during the second successive firing to form readily 'vitrifiable compounds at readily attainable temperatures.

most neutral, though refractoryand otherreaches wise most desirable rare earth om'ds of thorium, zirconium, lanthanium, etc.

Ceramic insulators can thus be constructed exclusively from oxids of only the trivalent and tetra-valent elements and free from easily electrolyzed and slag forming mono-valent alkali elements or the highly basic di-valent elements.

Zirconium oxi'd is at present the cheapest of the suitable neutral earth oxids and I have manufactured many refractory spark plug insulating structures containing 60 to 70% commercial zirconia that have proved in actual use over many months to Withstand the conditions of service where the best grades of porcelain fail. Zirconia insulators have an insulating about 100 times less than cold'porcelain 0r silicates, but are much better than porcelain when hot, and for voltages less than 10,000 to 11,000 volts will probably prove satisfactory'where an inexpensive device is required.

Having described my invention, what I claim is:

1. An electric spark plug having an improved structure for supporting and insulat being mg the electrodes non-fragile, resistant to sudden changes of temperature and having high dielectric re sistance when hot, consisting of a ceramic structure comprising zirconium and thorium compounds.

2. An electric spark'plug having a new insulating structure of great mechanical strength and infrangibility under sudden variations insulating resistance at high temperature consisting of a ceramic structure comprising characterized by resistance when coldof temperature and high electric Y zirconium compounds as its principal constituent.

3. A new electric spark plug having an. insulator consisting of a ceramic structure having great mechanical strength and heat resisting properties and high dielectric insulating resistance at high temperatures containing only the desirable neutral earth oxid such as lanthania and characterized by the absence of objectionable silica.

4. A new electric spark plug having an insulator having great mechanical strength and heat resisting roperties and high di electric insulatin peratures, consistlng of a ceramic structure composed of mixtures of desirable neutral earth oxids such as zirconia and characterized by the absence of the element silicon in any of its forms.

5. An improved spark plug having an insulator composed valent and tetra-valent earth oxids, such as lanthanium, thorium, zirconium and didym- 111m.

6. The improved electric spark plug having an insulator distinguished from known insulators by its composition being ractically free from alkalis and silica.

7. An electric sparkplug having an proved insulator conslsting of a ceramic structure composed principally of neutral tri-valent and tetr -valent earth oxid compounds and including cerium compounds.

In testimony whereof, I have signed my name to this specification this the 31st day of May, A. D. 1918.

CHARLES KNOX HARDING.

exclusively of neutral tri- 

